Electronic railway track circuit



Dec. 9, 1958 J. E. HILLIG ELECTRONIC RAILWAY TRACK cmcurr Sheefls-Sheet 1 mm mm E fin.

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' Aa'rommi Filed Jan. 28 1954 Dec. 9, 1958 Filed Jan. 28, 1954 .1; E. HlLL lG 2,863,993

ELECTRONIC RAILWAY TRACK CIRCUIT 2 Sheets-Sheet 2 177 3 ila J x L 25 12 I" I If?""' VT] I2 nyz.

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HIS Arrow United States Eatent Office 2,863,993 Patented Dec. 9, 1958 2,863,993 ELECTRONIC RAILWAY TRACK CIRCUIT John E. Hillig, Philadelphia, Pa., assignor to Westinghouse Air Brake Company, Wilmerding, Pa., a corporation of Pennsylvania Application January 28, 1954, Serial No. 406,627 2 Claims. (Cl. 246-130) My invention relates to improvements in railway track circuit apparatus, and more particularly to electronic apparatus for checking track occupancy, and has for one of its principal objects an improved arrangement for the automatic control of highway crossing signals.

Where a highway crossing intersects a stretch of railway track near a station at which certain of the trains may stop for indeterminate times, it is customary to provide means for causing the operation of the highway crossing warning signals to be interrupted after a train has occupied an approach section for a predetermined period of time, in order that highway traffic may proceed over the crossing if a train in approach to the crossing has stopped at the adjacent station. It has previously been proposed to cut out the operation of the signals by the operation of a time element relay governed by the track relay of the approach section, in such manner that when the track relay became deenergized, the time element relay would be operated and at the end of its timing cycle, would cut out the operation of the warning signals.

Such an arrangement, while fulfilling all the requisites for normal operation, is open to a very serious objection. If, for some reason, such as a broken rail or exhausted battery, the track relay should become deenergized, the apparatus would operate through its timing cycle and thereafter keep the crossing signals out of operation for all subsequent train movements, a distinctly hazardous condition.

An important feature of my invention is the provision of novel and improved apparatus for controlling a crossing signal, such, for example, as by raising the gates guarding the crossing near a station when a train makes an abnormally long station stop to load and unload passengers.

Another feature or objective of my invention is the provision of new and improved timing circuits for controlling a highway crossing signal.

Another objective is the provisionof new and improved apparatus having a-track occupancy detector for a highway crossing signal control system which will interrupt the operation of the highway crossing signal when a train makes an abnormally long stop at a station adjacent the highway crossing.

A further objective is the provision of a new and improved electronic circuit for checking track section occupancy.

Still a further objective of my invention is the provision of a new and improved electronic track section occupancy checking circuit which is substantially unresponsive to breaks in the track circuit such as might be caused by a broken track rail.

Other features, objects, and advantages of my invention will appear after a study of the accompanying specification when taken in connection with the accompanying drawings, in which:

Fig. 1 is a diagrammatic view of one form of apparatus according to a preferred embodiment of the invention; and

Fig. 2 is a diagram illustrating the operation of the 21pparatus shown in Fig. 1.

Similar reference characters refer to similar parts in each of the two views.

In practicing my invention, I provide, in combination with a stretch of railway track intersected by a highway crossing, a highway crossing signal governed by a signal control relay, which relay is normally under the control of a track relay associated with an approach section of track leading to the crossing. A tube relay governed by an electron discharge tube is arranged to become picked up when and only when a train shunt is effective in the approach section. This tube relay governs a time delay device, or time element relay, in such manner that the time delay relay picks up its contacts at the end of a predetermined time interval after the tube relay picks up. The pickup of the time element relay results in the by-passing of the approach track relay contacts in the energizing circuit for the control relay, so that the operation of the highway crossing signal is interrupted after a predetermined time interval. To restart the operation of the signal, I provide sound responsive means, which, when actuated by sounds having a predetermined characteristic, releases the time element relay and thereby restarts the operation of the signal.

Referring now to the drawings, and in particular to Fig. 1 thereof, the reference characters 1a and 1b designate the track rails of a stretch of track over which traflic normally moves in the direction indicated by the arrow, this stretch being divided by the usual insulated rail joints 6 into an approach section of track designated by the reference character ET, which it is understood has a station, not shown, adjacent thereto, and a center section of track designated by the reference character CT, which center section has a highway crossing thereover, a highway crossing signal XS being located at the intersection. Although the highway crossing signal XS is here shown as a conventional bell, it is understood that any suitable highway crossing signal device could be employed, such as, for example, power operated gates or flashing light signals of the type well known in the art.

Each of the track sections CT and ET is provided with a direct current neutral track circuit of conventional type, the track circuit for section CT including the battery CTB connected across the rails of the section at the righthand end thereof and the track relay CTR connected across the rails of the section at the left-hand end thereof.

The track circuit for section ET includes the track battery ETB which is normally connected across the rails at the right-hand end of the section, and the track relay ETR connected across the rails at the left-hand end of the section. The apparatus also includes a control relay XR for governing the operation of the crossing bell XS, a track repeater relay ETPR which is governed by a circuit arranged to energize this relay when track relay ETR is released, a coding device CT having contacts which, when connected across a source of suitable energy, operate from a first to a second position at some predetermined rate, such as, for example, 75 times per minute; a time element relay TER, having contacts which are arranged to operate from their released to their picked-up position after a predetermined time interval has elapsed following the energization of the time element relay winding; a stepping switch SSW, having conventional operating and stick windings for operating a stepper arm 9 to a plurality of different contact positions, and equipped with suitable biasing means to return the stepper arm to its initial position when both the control and stick windings are do energized; a repeater relay SPR for the contacts of the stepping switch; a microphone 17 which is mounted adjacent the track to pick up blasts from train whistles, and

connected through a conventional amplifier 16 to energize a relay ZR each time that sound of a predetermined characteristic is supplied to the microphone 17; and an arrangement including the electron discharge tube VT1 and a tube relay ER, together arranged so thatthe tube .VlElis fired and the relay ER is picked up vhenatrainoccupies any portion of the section ET.

In addition to the foregoing apparatu,s,various power supplies are provided for furnishing energy for the operation of the apparatus, including transformers such as transformer T1 for supplying energy to the clectron.tube circuits, energized from a suitable alternating current source, not shown, the terminals of which are designated by the reference characters BX and NX, and a low. voltage battery designated by the reference character LB having positive and negative terminals indicated by the 'eference characters B and N, respectively, for furnishing energy for the operation of various of the relays.

Having described the apparatus embodying my invention in general, I shall now describe its operation under various conditions.

As shown in the drawings, with no train occupying sections ET and CT, relay CTR is picked up by energy supplied thereto over the rails of section CT. Track relay ETR is also picked up at this time by energy supplied by a circuit which may be traced from the positive terminal of battery ETB, over back contact ofrelay ETPR, rail 1b of section ET, through the winding of relay ETR, rail 1a of section ET, and over back contact b of relay ETPR to the negative terminal of battery ETB.

With the contacts of relays CTR and ETR picked up, a circuit is established for energizing the winding of relay XR, which circuit may be traced from terminal B over front contact b of relay ETR, front contact a of relay CTR, and the winding of relay XR to terminal N. Since relay XR is picked up, its contact a interrupts an obvious circuit for supplying energy to the crossing signal XS, so that this signal is inactive at this time. Relay ETPR is released at this time, and, accordingly, the coding device 75CT is deenergized since front contact a of relay ETPR is open. A circuit including front contact (1 of relay ETPR for supplying alternating current energy to an electron tube apparatus and the amplifier circuit is also interrupted at this time. Transformer T2 is shown as having its primary winding P2 continuously connected to the terminals BX and NX of the source of alternating current energy, so that its secondary winding S5 continuously supplies energy to the heater 15 of the electron discharge tube VT1. Thus the tube is maintained in condition for operation when the circuits associated therewith are energized from the transformer T1. Since the amplifier 16 has current supplied thereto over the connection including front contact d of relay ETPR, this amplifier will be deenergized at this time so that relay ZR will be released. Thecircuit for supplying energy to the operating winding of the stepping switch SSW is open at front contact a of relay ZR, and the circuit for supplying energy to the stick winding of the stepping switch SSW is open at front contact b of relay TER, so that the stepping arm 9 of stepping switch SSW occupies its normal position, as shown, in which it establishes the connection with stationary contact -1. A circuit for energizing relay SPR is closed at this time and may be traced from terminal B at front contact 0 of relay CTR, over the arm 9 of stepping switch SSW, stationary contacts 1, 2, 3, and 4 of stepping switch SSW, and through the winding of relay SPR to terminal N. The tube relay ER is deenergized at this time, since the tube VT1 is not supplied with energy from the transformer T1 because contact (1 of relay ETPR is open.

Let it now be assumed that a train moving from left to right toward the crossing enters section ET. The wheels and axles of the train will shunt the supply of direct current energy from battery ETB to the winding of relay ETR, with the result that relay ETR will release its contacts. When contact b of relay ETR releases, the circuit previously traced for energizing relay XR is interrupted, and the consequent release of relay XR establishes the circuit over contact a of this relay for energizing the crossing signal XS, which then commences to operate to warn users of the highway of the approach of the train. The release of contact a of track relay ETR establishes the circuit for supplying energy to the track repeater relay ETPR, so that its contacts pick up. When contact d of relay ETPR picks up, alternating current energy is supplied by an obvious circuit to the primary winding P1 of transformer T1 and to the amplifier 16 associated with microphone 17. With contact a of relay ETPR picked up, the winding of the coding device 75CT is supplied with energy, so that the contacts a, b, c, and d of coding device 75CT will be recurrently operated between their released and pickedup positions. Each time that the contacts a and b of coding device 75 CT are released, direct current energy is supplied to the rails 11: and 1b of track section ET from the battery ETB, by a circuit which may be traced from the positive terminal of battery ETB, over back contact b of coding device 75CT, and from contact c of relay ETPR to rail 1b vi a lead 28, while the negative terminal of battery ETB is connected to rail In over back contact a of coding device 75CT and front contact b of relay ETPR and lead 27. When the contacts of coding device 7501 are picked up, the rails 1a and 1b are connected to a secondary winding S1 of transformer T1 by a circuit which includes front contacts 12 and c of relay ETPR, front contacts a and b of coding device 75CT, and the resistor R1. It will be apparent from the foregoing that, at this time when the train occupies section ET and is advancing toward the crossing, section ET is recurrently supplied with impulses of alternating current energy from the secondary winding S1 alternated with impulses of direct current energy from battery ETB.

Considering now in detail the apparatus associated with the vacuum tube VT1 and the tube relay ER, an additional secondary winding S2 of transformer T1 has one terminal thereof connected to rail 1:: via lead 29, and is also connected to the cathode 14 01? the tube VT1 and to one terminal of the secondary S4 of transformer T1. The instantaneous polarities of the varioussecondary windings are shown in the conventional manner. Tube VT1 may be of the well-known shield-grid thyratron type. The other terminal of secondary winding S4 is connected to the control or first grid 13 of tube VT1 through resistor R6. The other terminal of secondary winding S2 of transformer T1 is connected to rail 1b of section ET by a circuit including front contact c of the coding device 75CT, the potentiometer R3, and the resistor R2, all in series, and lead 30. Preferably, but not necessarily, the track leads 29 and 30 are connected to the rails 1a and 1b, respectively, of section ET near the entrance end of the section, or at some intermediate point. The movable arm of the potentiometer R3 is connected to one terminal of the shield-grid 12 of the tube VT1, the other terminal of this grid being connected to one terminal of secondary winding S3 of transformer T1 with the opposite terminal of wind ing S3 being connected to the plate or anode 11 of tube VT1 by a circuit which includes front contact d of the coding device 75CT, resistor R and the winding of the tube relay ER. A capacitor C1 and resistor R4 are connected in series across the winding of tube relay ER to function as a snubbing circuit, so that the contacts of relay ER will be sufiiciently slow in releasing to bridge the intervals during which tube VT1 does not conduct current, as well as to bridge the intervals in which the contacts of coding device 75CT are in their released position, when the coding device 75CT is .recurrently operating as the result of the release of track relay ETR.

Relay ER is employed to govern the operation of the time element relay T ER which cuts out the operation of the crossing signal after a train has occupied the section ET for a predetermined length of time. Its control is established by a circuit which may be traced from terminal B at front contact a of relay ER, through the winding of relay TER, over front contact a of the stepping switch repeater relay SPR, through a normally closed push button 26, and over front contact b of relay CTR to terminal N. The relay TER is of the type which has contacts which become picked up after the end of a predetermined time interval following the energization of the relay, and which contacts thereafter remain in their picked-up position until the winding of the relay is deenergized. Accordingly, it may be seen that relay TER will be energized when the contacts of relay ER are picked up as the result of a train shunt in section ET, and after the relay TER picks up its con tacts, they will remain picked up until the relay SPR or relay CTR is released by the subsequent movement of the train, or by manual cancellation as the result of operation of the push button 26.

Let it now be assumed that the train which is moving from left to right through section ET is one which does not stop at the station, not shown, adjacent section ET.

At this time, energy is supplied to the rails of section ET from secondary winding S2 of transformer T1 each time that contact 0 of the coding device 75CT picks up. Because of the shunting effect of the wheels and axles of the train, alternating current energy will flow through the circuit which includes the secondary winding S2 of transformer T1, potentiometer R3 and resistor R2, the leads 29 and 30 and the wheels and axles of the train. Accordingly, a predetermined voltage drop will exist across the voltage divider comprising the resistor R2 and potentiometer R3, a portion of which voltage is supplied to the shield-grid 12 of the tube VT1 through the movable arm of the potentiometer. The parts are proportioned and arranged so that this voltage is just sufficient, in conjunction with the voltage on the control grid 13 supplied from secondary winding S4 by way of resistor R6, and the positive anode voltage applied at the same time from the secondary winding S3 over front contact d of coding device 75CT, to cause the tube VT1 to fire. Accordingly, on each positive alternation of the energy supplied from the secondary winding S3, the tube will fire to thereby supply energy to the winding of the tube relay ER so that this relay will pick up its contacts. The capacitor C1 and resistor R4 are proportioned and arranged so that the relay ER is rendered sufficiently slow in releasing to not only bridge the intervals during the negative alternations of the anode potential when the tube is not firing, but also to bridge the intervals in which the contact I of the coding device 75CT is open.

From the foregoing, it will be apparent, that, at this time with the train occupying section ET, the train shunt causes the vacuum tube VT1 to be recurrently fired each time that contact a of coding device 75CT is picked up, so that relay ER is continuously picked up at this time.

With relay ER picked up, its front contact a establishes the circuit previously traced for energizing the time element relay TER, but as hereinbefore pointed out, relay TER does not pick up its contacts until after the expiration of a predetermined time interval, say, for example, twenty seconds. Since it is assumed that the train in question is a high speed train not scheduled to stop at the adjacent station, the train will have passed through section ET and entered track section CT before the predetermined time interval required for relay TER to pick up its front contacts will have elapsed. When the train enters section CT, relay CTR is deenergized and its front contact a additionally interrupts the circuit for supplying energy to the winding of relay XR, so that this relay remains released and accordingly the crossing signal remains in operation. Additionally, the release of contact b of relay CTR interrupts the circuit for energizing the winding of relay TER, so that this relay is restored to its normal condition.

When the rear of the train vacates section ET, the first impulse of direct current energy supplied to the rails 1a and 1b over the track leads 27 and 28 from battery ETB, including the circuit governed by front contacts b and c of relay ETPR and the back contacts a and b of coding device CT, will flow over the section rails to cause relay ETR to pick up its contacts. When contact a of relay ETR picks up, the circuit for energizing relay ETPR will be interrupted, so that its contacts will release. With contacts b and c of relay ETPR released, direct current energy will be continuously supplied to the rails 1a and 1b of section ET so that track relay ETR will remain continuously energized.

Although front contact b of relay ETR is now picked up, the circuit for energizing relay XR will continue to remain interrupted by the front contact a of relay CTR in view of the fact that the rear of the train still occupies section CT.

The release of relay ETPR deenergizes the coding device 75CT, and additionally deenergizes the transformer T1 and the amplifier 16, so that relay ER reeases and this apparatus is restored to its normal condition.

When the train vacates section CT, relay CTR will pick up and its front contact a will reestablish the circuit for energizing relay XR, the consequent pickup of which deenergizes the warning signal XS. The apparatus is thus restored to its normal condition as previously described.

Considering now the operation with a train scheduled to stop at the station adjacent section ET, the entrance of the train into section ET will cause the release of track relay ETR, the release of relay XR with the consequent operation of the crossing signal XS, and the energization of the electronic equipment so that relay ER becomes picked up as previously described. However, with the train remaining in section ET for a time longer than the operating time of the time element relay TER, it will be seen that relay TER will pick up its contacts with the train still occupying section ET. When contact a of relay TER picks up, it establishes a circuit for energizing relay XR which may be traced from terminal B at front contact a of relay TER, over front contact a of relay CTR, and through the winding of relay XR to terminal N. Accordingly, relay XR will pick up and thereby stop the operation of the warning signal, so that highway traffic may pass over the crossing while the train is stopped at the station.

This condition will persist so long as the train remains in section ET since the time element relay TER will continue to be energized by the previously traced circuit including front contact A or tube relay ER.

When the train is ready to depart, the engineman will sound the usual whistle signal for recalling the fiagman to the train preparatory to departure, this whistle signal consisting, for example, of four long blasts of the whistle with a short pause between each blast. The sound of the whistle blasts is picked up by the microphone 17, and amplified by the amplifier 16 so that relay ZR is picked up and released four successive times, in response to the four successive whistle blasts. Each time that relay ZR picks up, its front contact a establishes an obvious circuit for supplying energy to the operating Winding of the stepping switch SSW. As previously pointed out, the stepping switch SSW is constructed and arranged in such manner that each time that energy is supplied to the operating winding thereof, the movable arm 9 of the switch advances one position along the stationary contacts 1, 2, 3, 4, and 5. The stick winding of stepping switch SSW is energized at this time by the circuit including front contact b of relay TER, so that tho arm 9 of the stepping switch is retained in the position to which it was last operated. The energization of the stick winding of stepping switch SSW will retain the movable arm 9 of the switch in the position to which it was last operated when the supply of energy to the operating Winding is interrupted by the release of contact a of relay ZR. It is to be pointed out that the amplifier 16 may or may not be necessary, and if a suitable microphone and a sutficiently sensitive relay are employed, the amplifier will not be required.

From the foregoing, it will be seen that at this time the arm 9 of stepping switch SSW is successively operated through the stationary contacts 1, 2, 3, and 4 to the fifth position, as a result of the pickup of the four whistle blasts of the train preparing to depart from section ET. When the arm 9 of stepping switch SSW reaches the position designated by the reference character 5, it establishes an additional stick circuit for maintaining the arm of the stepping switch in that position, which stick circuit includes the front contact c of relay CTR, the movable arm 9 and stationary contact 5 of the stepping switch SSW and the stick winding of the stepping switch. When the movable arm 9 moves from contact 4 to contact 5, the circuit for supplying energy to the stepping switch repeater relay SPR is interrupted, and as a result contact a of relay SPR is released. The release of this contact interrupts the circuit for energizing the time element relay TER, and accordingly contacts a and b of relay TER release. Contact [1 of relay TER thereby interrupts the original stick circuit for the stepping switch SSW, but as hereinbefore pointed out, the movable arm 9 and stationary contact 5 of the stepping switch SSW cooperate at this time to maintain the stepping switch in the fifth position. The release of contact a of relay TER interrupts the circuit for supplying energy to the winding of relay XR since contact b of relay ETR is released at this time by virtue of the train occupying section ET, so that the warning signal XS is again placed in operation. When the train starts and moves into section CT, the contact a of relay CTR will release and maintain the relay XR deenergized, so that the crossing signal XS continues to operate. The release of contact c of relay CTR will interrupt the circuit for supplying energy to the stick winding of stepping switch SSW, and, accordingly, the biasing means, not shown, for the stepping switch SSW will restore the movable arm 9 to its initial position.

When the rear of the train vacates section ET, the track relay ETR will pick up upon the first impulse of direct current supplied thereto over the section rails from battery ETB, and will release the repeater relay ETPR, with subsequent restoration of the apparatus including the vacuum tube VT1 and the tube relay ER to its original condition. The picking up of relay ETR again closes front contact I) of this relay, in the circuit for energizing relay XR, but the energizing circuit for relay XR is maintained deenergized at this time at front contact a of relay CTR, since the rear of the train still occupies section CT. However, when the rear of the train vacates section CT, relay CTR will again pick up. and the circuit originally traced for energizing relay XR will become established, so that relay XR will pick up and cut off the operation of the warning signal XS. The apparatus is thus restored to its normal condition.

In the event of failure or improper operation of the sound-actuated apparatus, so that relay SPR does not release to release the time element relay TER. the manually operated push button 26 may be operated by a member of the train crew, this operation interrupting the circuit governing relay TER, so that the highway crossing signals may again be set into operation.

As has been previously pointed out, it is essential that erroneous operation be guarded against in the case of a track circuit failure such as an exhausted battery, a broken track lead, or some other failure which would cause the track relay ETR to release and remain released. Under these conditions, it is necessary to insure that time element relay TER will not operate falsely at this time to cut off the protection afforded by track section ET in the control of the crossing signal XS; otherwise, the warning of the approach of a train might not be given highway tratfic by operation of signal XS until the train had reached section CT. Accordingly, it is necessary to insure that the time element relay TER will not be operated except because of the actual shunting effect of a train in section ET, and will not be operated by a failure of the direct current track circuit including the track relay ETR. The electronic track occupancy circuit forming a portion of my invention including the vacuum tube VT1 and the tube relay ER is arranged in such manner that the tube VT1 cannot fire to thereby pick up relay ER unless a train shunt is present in section ET, broken rails or other defects not having the capability of causing false operation of tube relay ER. Such operation is obtained by the novel arrangement of the apparatus in such manner that the bias voltages which govern the operation of tube VT1 can only be changed to fire the tube by the presence of a train shunt in section ET and not by an open circuit failure such as might be caused by the breakage of a track rail. This operation may be better understood by reference to Fig. 2 which is a simplified illustration of the apparatus shown in Fig. l, to illustrate the relationship of the various voltages supplied to the tube VT1.

Considering first the case in which there is no train occupying the section, it is to be understood that under this condition the train shunt represented by the wheels and axle 25 across the rails 1a and 1b is removed. Although the shunt 25 is absent, due to the absence of a train in track section ET, the ballast resistance of the track circuit represented by the resistor R12 in parallel with the winding of relay ETR may provide a path across the rails of the order of, for example, 2 ohms. At the same instant that the left ends of secondaries S1 and S2 are negative as viewed in Fig. 2, the voltages on the control grid 13 and anode 11 are positive. However, the positive bias on grid 13 is insufficient to cause the tube VT1 to fire, if the arm of potentiometer R3 is adjusted to a position or setting where the negative voltage on grid 12 has at least a predetermined value. The voltage on grid 12 isinfiuenced by the energy supplied from the secondary S2, minus the voltage drop across the portion of the potentiometer R3 between the arm and secondary S2. This voltage depends on the current through the potentiometer which also flows through ballast resistance R12 and the winding of relay ETR and is influenced by the fact that the ballast resistance R12 and the winding of relay ER are also operatively connected to secondary S1 through the resistor R1. The movable arm of the potentiometer R3 is adjusted in the absence of a train to a setting which will just cause the tube VT1 to be extinguished, or not fired.

Assume now that a train enters section ET, so that the train shunt which is represented by the wheels and axle 25 across the rails 1a and 112 provides a very low resistance path, such, for example, as 0.06 ohm, across the rails of the section. The effect of shunting the ballast resistance and the winding of relay ETR by the train shunt is such as to make the potential at the potentiometer arm and grid 12 less negative with the result that tube VT1 will fire, and, as previously pointed out, will cause the tube relay ER to be energized.

Moreover, a break in one or the other or both of the section rails of section ET will not result in false operation of the apparatus since, under these conditions, the tube VT1 is also prevented from firing. A broken rail at X would make the voltage on the arm of potenti ometer R3 more negative. A broken rail at Y would make the voltage on the arm of potentiometer R3 more negative also. Accordingly, the tube relay ER cannot pick up under these circumstances, and consequently relay TER cannot be energized to thereby cut out the contacts of relay ETR in the circuit for governing the operation of the warning signal.

Although I have herein shown the application of the apparatus embodying my invention as applied to a stretch of railway track in which traffic moves in only one direction therethrough, it will be understood by those skilled in the art that the arrangement may be as readily applied to stretches of railway track in which traific moves therethrough in both directions, the control circuits for the opposite direction being arranged in a similar manner.

The following list is illustrative of the values of the various components and voltages which may be employed in the electronic portions of the circuit arrangement, to provide a suitable arrangement of apparatus which will operate in the manner previously described.

Tube type2D21 R1 ohrns 10 R2 do 3 R3 do 7 R4 do 1000 R5 do 5000 R6 do 2500 C1 mfd 8 Transformer T1 voltages Volts S4 12-24 Transformer T2 voltages Volts Although I have herein shown and described only one form of electronic railway track circuit apparatus embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. In combination, a stretch of railway track formed into at least two track sections and intersected by a highway at the second of said section, a first track circuit for the first section including a first track relay having front and back contacts, a second track circuit for the second section including a second track relay having a plurality of front contacts, a crossing signal, a signal relay for said signal, means for energizing said signal relay through a front contact of said first track relay and one of said plurality of front contacts of said second track relay, said signal relay causing operation of the signal when a train approaching the intersection enters the first track section, control means including an electron discharge tube circuit having a relay therein, said control means being connected to the first track section and under the control of a train approaching the intersection when the train enters the first track section, time element means including a time delay relay under the control of the relay in said control means and another one of said plurality of front contacts of said second track relay and effective when energized for a predetermined time interval after the train enters the first track section to operate said signal relay to discontinue the operation of said signal, and sound-operated means controlled by the back contact of said first track relay and efiective when energized by a sound signal of predetermined characteristics to operate said signal relay to restore said signal to operation.

2. In combination, a stretch of railway track formed into at least two track sections and intersected by a highway at the second section, a highway crossing signal located at the intersection, a first track circuit for the first track section including a first track relay having front and back contacts, a second track circuit for the second track section including a second track relay having a plurality of front contacts, a signal relay for said signal, said signal being adapted to be energized while the signal relay is deenergized, circuit means for energizing the signal relay through a front contact of said first track relay and one of said plurality of front contacts of said second track relay, said signal relay causing operation of the signal when a train approaching the intersection enters the first track section, time element means including a time delay relay having at least a front contact, additional circuit means for energizing said signal relay through the front contact of said time delay relay, track occupancy checking means comprising an electron discharge tube circuit including a relay, said checking means being connected to the first track section and under the control of a train approaching the intersection when the train enters the first track section, said time delay relay being under the control of the relay in said electron discharge tube circuit and another one of said plurality of front contacts of said second track relay and effective when energized for a predetermined time interval after a train enters the first track section to energize said signal relay and stop the operation of said signal, and sound-operated means controlled from the back contact of said first track relay and effective when energized by a sound signal of predetermined characteristics to deenergize said signal relay and restore said signal to operation.

References Cited in the file of this patent UNITED STATES PATENTS 1,805,167 Fitzgerald May 12, 1931 1,868,489 Barry July 26, 1932 2,071,995 Allen Feb. 23, 1937 2,106,680 Reichard Jan. 25, 1938 2,554,460 Hillig et al. May 22, 1951 2,578,347 Gagnaire Dec. 11, 1951 2,664,498 Martin Dec. 29, 1953 

